Re: [PATCH 2/5] mm, memcg: narrow the scope of percpu_charge_mutex
From: Roman Gushchin <hidden>
Date: 2021-07-30 03:07:17
Also in:
linux-mm, lkml
On Thu, Jul 29, 2021 at 08:57:52PM +0800, Miaohe Lin wrote:
quoted hunk ↗ jump to hunk
Since percpu_charge_mutex is only used inside drain_all_stock(), we can narrow the scope of percpu_charge_mutex by moving it here. Signed-off-by: Miaohe Lin <redacted> --- mm/memcontrol.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 6580c2381a3e..a03e24e57cd9 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c@@ -2050,7 +2050,6 @@ struct memcg_stock_pcp { #define FLUSHING_CACHED_CHARGE 0 }; static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock); -static DEFINE_MUTEX(percpu_charge_mutex); #ifdef CONFIG_MEMCG_KMEM static void drain_obj_stock(struct obj_stock *stock);@@ -2209,6 +2208,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages) */ static void drain_all_stock(struct mem_cgroup *root_memcg) { + static DEFINE_MUTEX(percpu_charge_mutex); int cpu, curcpu;
It's considered a good practice to protect data instead of code paths. After the proposed change it becomes obvious that the opposite is done here: the mutex is used to prevent a simultaneous execution of the code of the drain_all_stock() function. Actually we don't need a mutex here: nobody ever sleeps on it. So I'd replace it with a simple atomic variable or even a single bitfield. Then the change will be better justified, IMO. Thanks!